Fan blades are a key component of gas turbine engines such as jet engines and serve to guide airflow and draw air into the engine, as well as to protect the engine from environmental hazards. In modern jet engines they can also have a significant role in providing thrust by propelling air through the engine. The fan blades are generally the first component of the engine to contact incoming air. Thus they contribute greatly to setting up the airflow through the engine. Aircraft propeller blades provide the motive force for a propeller driven aircraft. They convert rotary motion from an engine into a force to drive the aircraft forward. As with fan blades they are the first component to contact the incoming air and the action of the propeller blades in generating thrust and guiding airflow is highly important to the operation of the aircraft.
Airfoil blades such as fan blades and propeller blades are exposed to outside factors such as varying air temperatures as well as bird impact and other damage from foreign objects. In addition, the blades must operate within the same envelope as the aircraft or gas turbine engine itself, which can include extremes of temperature, pressure, and airspeed. As a consequence the structure and manufacture of the blades is of great importance. The blades must be light and strong, as well as being tough enough to avoid or minimise damage when there is a high speed impact from a foreign object.
Various methods for manufacture of composite blades exist. For example, it is known to build up textile layers in a mould to form the shape of the blade, with the textile layers being pre-impregnated with a suitable matrix material such as a thermoplastic resin (‘pre-preg’ textiles) or with the matrix material being applied to each layer as the layers of textile are built up. Resin transfer manufacturing (RTM) techniques are also used, where the textile layers are prepared in a mould absent any kind of matrix material, and the matrix material is then injected into the mould or drawn into the mould via vacuum in order to surround the textile with the matrix. It is known for manufacturing processes to include a thermoforming and/or a curing stage after the textile and matrix material have been formed into a required shape. For example, see U.S. Pat. No. 871,556 where a turbine fan blade is formed via thermoforming with moulding steps using heat and pressure.